1. Field of the Invention
The present invention relates to a mobile communication terminal used in a mobile communication system such as a cellular phone system, a wireless LAN, etc., and incoming data detecting method and program, which are executed in the mobile communication terminal, and more particularly, to a mobile communication terminal, which extends a standby time with a discontinuous reception control, in a CDMA (Code Division Multiple Access) system, and incoming data detecting method and program, which are executed in the mobile communication terminal.
2. Description of the Related Art
Conventionally, the battery of a mobile communication terminal is saved with a discontinuous control in a W-CDMA (Wideband CDMA) mobile communication system.
With the discontinuous control, a mobile communication terminal is controlled with a PICH (Paging Indicator CHannel), and a PCH (Paging CHannel) that is a transport channel mapped on an SCCPCH (Secondary Common Control Physical CHannel).
With the PICH, a short PI (Paging Indicator) for notifying a mobile communication terminal of whether or not incoming information exists is transmitted. Only if it is notified to the mobile communication terminal that the incoming data exists, the mobile communication terminal receives the PCH corresponding to the PI. Namely, the mobile communication terminal receives the PICH prior to the reception of the PCH. The PICH is a channel for transmitting PI (Paging Indicator) data for which error correction coding (channel coding) is not made. Then, the mobile communication terminal determines whether or not Paging is made based on the PI data received with the PICH, and executes a decoding/reproduction process for incoming data by receiving the PCH only if the incoming data is determined to exist. As a result, the mobile communication terminal receives the PCH only if it verifies based on the PICH that the incoming data exists. Otherwise, the mobile communication terminal does not receive the PCH.
The discontinuous reception cycle of a frame in which a PI is mapped is specified with broadcast information of a base station as DRX Cycles Length (discontinuous cycle). The mobile communication terminal also executes in parallel a level measurement process for detecting a cell transition upon receipt of a PI. Furthermore, the mobile communication terminal executes a cell search process for detecting a neighboring cell in a suitable cycle in consideration of the influence of current consumption.
For example, the invention disclosed by Japanese Patent Publication No. 2004-112148 uses broadcast information cached beforehand if a CRC (Cyclic Redundancy Check) results in NG (CRC-NG) upon receipt of broadcast information when a handover is made during the standby state of a mobile communication terminal. As a result, both the duration for receiving broadcast information and the operation time are shortened, whereby power consumption can be reduced. Moreover, the length of time required for a cell reselection can be shortened because the cell reselect ion can be efficiently made in an environment where the cell reselection often occurs. This increases an incoming rate. The cell reselection is an operation for selecting one optimum reception wave when a mobile communication terminal detects a plurality of reception waves during its transition to a standby state.
The timing of making a conventional cell reselection is described here.
FIG. 1 is a schematic diagram showing a relationship between base stations, service areas, and a mobile communication terminal in conventional technology, whereas FIG. 2 is a schematic diagram showing a relationship between a reception level and a cell reselection in the conventional technology.
In FIG. 1, a mobile communication terminal 10 makes a wireless communication with a first base station 20, which offers a first service area 21, within the first service area 21, and makes a wireless communication with a second base station 30, which offers a second service area 31, within the second service area 31. In an area where the first service area 21 and the second service area 31 overlap, the mobile communication terminal 10 can make a wireless communication with the first base station 20 or the second base station 30 by receiving Paging from the first base station 20 or the second base station 30 in accordance with the position of the mobile communication terminal 10.
When the mobile communication terminal 10 moves from the first service area 21 to the second service area 31, a reception level from the first base station 20 within the first service area 21 drops with the elapse of time during which the mobile communication terminal 10 is moving from the first service area 21 to the second service area 31, and a reception level from the second base station 30 within the second service area 31 rises with the elapse of time during which the mobile communication terminal 10 is moving from the first service area 21 to the second service area 31.
While the reception level within the first service area 21 is higher than that within the second service area 31, the mobile communication terminal 10 makes a wireless communication with the first base station 20. Also in a time period from a time t1 at which the reception level within the first service area 21 and that within the second service area 31 are reversed to a time t2 at which the reception level within the second service area 31 becomes higher than that within the first service area 21 by a predetermined value or more, the mobile communication terminal 10 makes a wireless communication with the first base station 20.
At the time t2 when the reception level within the second service area 31 becomes higher than that within the first service area 21 by the predetermined value or more, the mobile communication terminal 10 still makes a cell reselection, and starts to make a wireless communication with the second base station 30.
However, the conventional technology has a problem that the mobile communication terminal cannot receive incoming data if it fails to receive a PCH (CRC-NG) despite receiving incoming information with a PI, for example, when the reception environment (active cell) of the mobile communication terminal is degraded.
FIG. 3 is a schematic diagram for explaining the case where the mobile communication terminal cannot receive incoming data in the conventional technology.
As shown in FIG. 3, the mobile communication terminal 10 conventionally fails to receive incoming data by attempting to make a wireless communication with the first base station 20 although its reception environment is degraded by a drop in the reception level within the first service area 21, when Paging from the first base station is made in the time period from the time t1 at which the reception level within the first service area 21 and that within the second service area 31 are reversed to the time t2 at which the reception level within the second service area 31 becomes higher than that within the first service area 21 by the predetermined value or more.
FIG. 4 is a flowchart showing incoming data detection process executed with the conventional technology.
This process is described by assuming the case where the mobile communication terminal 10 moves from the first service area 21 to the second service area 31.
Initially, in step S41, the mobile communication terminal 10 receives a paging indicator (PI) within a paging indicator channel (PICH) in the first service area 21. The PICH is a channel for transferring a paging indicator that is transmitted to notify that incoming data (local group incoming data) exists for any of mobile communication terminals 10 within a service area offered by a base station from the base station to which the mobile communication terminal 10 registers its position. Then, if the mobile communication terminal determines in step S42 that the local group incoming data exists (“YES” in step S42), it receives a paging channel (PCH) transmitted immediately after (for example, after approximately a little less than two milliseconds) the PI. The PCH is a channel for notifying whether or not local group incoming data is paging to the local mobile communication terminal 10.
Next, if the mobile communication terminal 10 determines that it fails to obtain local incoming information (CRC-NG) due to the unsuccessful reception of the PCH caused by the reception environment degraded by the moving of the mobile communication terminal 10 from the inside of the first service area 21 to its outside (“NO” in step S44), the mobile communication terminal 10 receives a retransmitted PI in step S45. If the mobile communication terminal 10 determines in step S46 that the local incoming data exists (“YES” in step S46), it receives a PCH transmitted immediately after the PI.
If the mobile communication terminal 10 determines in step S48 that it again fails to receive the PCH (“NO” in step S48), it determines in step S49 that a connection is unsuccessfully made.
If the mobile communication terminal 10 determines in S44 or S48 that it successfully receives the PCH (CRC-OK) (“YES” in step S44 or S48), it issues a connection request in step S50, and makes a connection in step S51.